The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
Air is drawn into an engine through an intake manifold. A throttle valve controls airflow into the engine. More specifically, the throttle valve adjusts throttle area, which increases or decreases airflow into the engine. As the throttle area increases, the air flow into the engine increases. A fuel control system adjusts the rate that fuel is injected into the engine cylinders to provide a desired air/fuel mixture to the cylinders and/or to achieve a desired torque output. Increasing the amount of air and fuel provided to the cylinders increases the torque output of the engine.
The air/fuel mixture is combusted within one or more cylinders of the engine. In spark-ignition engines, spark initiates combustion of the air/fuel mixture provided to the cylinders. In compression-ignition engines, compression of the air/fuel mixture in the cylinders combusts the air/fuel mixture. Spark timing and airflow are the primary mechanisms for adjusting the torque output of spark-ignition engines, while fuel flow is the primary mechanism for adjusting the torque output of compression-ignition engines. Incomplete, or partial combustion of the air/fuel mixture during engine start may cause the engine to vibrate.
During engine shutdown, a rotation direction of a crankshaft in the engine may be reversed before the crankshaft stops. In turn, a piston coupled to the crankshaft may stop near top dead center (TDC) before movement of the piston is reversed. This reversal of piston movement during engine shutdown is referred to as rock back. As the piston rocks back, the piston draws exhaust gas into the cylinder in which the piston is disposed. Exhaust gas is also be drawn into an intake manifold of the engine due to a pressure difference between the intake manifold and the cylinders. When the engine is restarted, exhaust gas flows from the intake manifold to the cylinder, and exhaust gas present within the cylinder may cause the cylinder to misfire which in turn may cause the engine and the passenger compartment to vibrate.
An engine control module (ECM) controls the torque output of the engine. Under some circumstances, the ECM shuts down the engine between vehicle startup (e.g., key ON) and vehicle shutdown (e.g., key OFF). The ECM selectively shuts down the engine, for example, to increase fuel efficiency (i.e., reduce fuel consumption). The ECM starts the engine at a later time.
While traditional stop-start systems for internal combustion engines are effective, there is room in the art for an improved stop-start system and method that ensures the appropriate amount of air and fuel are supplied to the cylinders for low-vibration engine start. Especially desirable, would be a stop-start system that performs under a wide variety of ambient conditions while reducing engine start vibration.